#include <stdio.h>

#define MAX_COST 100000 

int min(int a, int b) {
    return a > b ? b : a;
}

int dp[1101];

int main() {
    int C, N;
    scanf("%d %d",&C, &N);

    dp[0] = 0;
    for(int i=1; i<=C+100; i++) dp[i] = MAX_COST;

    while(N--) {
        int cost, man;
        scanf("%d %d",&cost, &man);

        for(int c=man; c<C+101; c++) dp[c] = min(dp[c], dp[c-man] + cost);
    }

    int ans = MAX_COST;
    for(int i=C; i<C+101; i++) ans = min(ans, dp[i]);

    printf("%d\n",ans);

    return 0;
}