题解 | 清楚姐姐买竹鼠

#include <stdio.h>
typedef long long ll;
int main() {
    ll a, b, x;
    scanf("%lld%lld%lld", &a, &b, &x);

    ll sum = 0;
    if(a*3 > b){
        ll res = x % 3;
        if(a*res < b)
            sum = b*(x / 3) + a*res;
        else
            sum = b*(x/3) + b;
    }
    else {
        sum = a*x; 
    }
    printf("%lld", sum);

    return 0;
}