#include <stdio.h>

int main(void){
    int A;
    long long B, N;
    int max, tmp;
    max = 0;

    scanf("%d%lld%lld", &A, &B, &N);
    for(int x = 1; x <= N; x++){
        tmp = (A*x/B) - (A*(x/B));
        if(tmp > max)
            max = tmp;
    }
    printf("%d\n", max);
    
    return 0;
}
