#include <stdio.h>
 
int main() {
    int N, M;
    scanf("%d %d", &N, &M);
 
    int package[M], single[M];
    for (int i = 0; i < M; i++) {
        scanf("%d %d", &package[i], &single[i]);
    }
 
    // 패키지 구매 vs 낱개 구매
    int min_package = package[0] * (N / 6) + single[0] * (N % 6);
    for (int i = 1; i < M; i++) {
        int cost = package[i] * (N / 6) + single[i] * (N % 6);
        if (cost < min_package) {
            min_package = cost;
        }
    }
 
    printf("%d\n", min_package);
 
    return 0;
}
 

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MTAgMwoyMCA4CjQwIDcKNjAgNA==

10 3
20 8
40 7
60 4