#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <math.h>

long long power(int base, int exp) {
    long long result = 1;
    for (int i = 0; i < exp; i++) {
        result *= base;
    }
    return result;
}

long long min_ll(long long a, long long b) {
    return a < b ? a : b;
}

int min_int(int a, int b) {
    return a < b ? a : b;
}

int solution(int tires[][2], int tiresSize, int changeTime, int numLaps) {
    int maxConsecutive = min_int(numLaps, 20);
    long long minTime[10][21]; // Assuming max 10 tires and 20 consecutive laps
    
    for (int i = 0; i < tiresSize; i++) {
        for (int j = 0; j <= maxConsecutive; j++) {
            minTime[i][j] = LLONG_MAX;
        }
    }
    
    for (int i = 0; i < tiresSize; i++) {
        int f = tires[i][0];
        int r = tires[i][1];
        long long time = 0;
        for (int j = 1; j <= maxConsecutive; j++) {
            time += (long long)f * power(r, j - 1);
            minTime[i][j] = time;
            if (time > changeTime + f) break;
        }
    }
    
    long long dp[1001]; // Assuming max 1000 laps
    for (int i = 0; i <= numLaps; i++) {
        dp[i] = LLONG_MAX;
    }
    dp[0] = 0;
    
    for (int i = 1; i <= numLaps; i++) {
        for (int j = 0; j < tiresSize; j++) {
            for (int k = 1; k <= min_int(i, maxConsecutive); k++) {
                if (minTime[j][k] != LLONG_MAX) {
                    long long changeCost = i > k ? changeTime : 0;
                    dp[i] = min_ll(dp[i], dp[i - k] + changeCost + minTime[j][k]);
                }
            }
        }
    }
    
    return (int)dp[numLaps];
}

int main() {
    char buffer[1000];
    fgets(buffer, sizeof(buffer), stdin);
    
    int tires[10][2];
    int tiresSize = 0;
    
    char* ptr = strchr(buffer, '[');
    if (ptr) {
        ptr++;
        while (*ptr && tiresSize < 10) {
            if (*ptr == '[') {
                ptr++;
                tires[tiresSize][0] = atoi(ptr);
                while (*ptr && *ptr != ',') ptr++;
                if (*ptr == ',') ptr++;
                tires[tiresSize][1] = atoi(ptr);
                tiresSize++;
                while (*ptr && *ptr != ']') ptr++;
                if (*ptr == ']') ptr++;
                while (*ptr && (*ptr == ',' || *ptr == ' ')) ptr++;
            } else {
                ptr++;
            }
        }
    }
    
    int changeTime, numLaps;
    scanf("%d", &changeTime);
    scanf("%d", &numLaps);
    
    int result = solution(tires, tiresSize, changeTime, numLaps);
    printf("%d\n", result);
    
    return 0;
}