E - Crested Ibis vs Monster

#include <iostream>
using namespace std;

unsigned long long INF=999999999999999999;

unsigned long long v[20001];
unsigned long long a[1001],b[1001];

int main()
{
    unsigned long long h,n,i,j,cnt,min1;
    cin>>h>>n;
    for(i=1;i<=n;i++){
        cin>>a[i]>>b[i];
    }
    for(j=0;j<=2*h;j++){
        v[j]=INF;
    }
    v[0]=0;
    for(i=1;i<=n;i++){
        for(j=0;j<=h;j++){
            cnt=0;
            if(v[j]!=INF){
                while(j+cnt*a[i]<h){
                    v[j+cnt*a[i]]=min(v[j+cnt*a[i]],v[j]+cnt*b[i]);
                    cnt++;
                }
                v[j+cnt*a[i]]=min(v[j+cnt*a[i]],v[j]+cnt*b[i]);
            }

        }
    }
    min1=INF;
    for(i=h;i<=2*h;i++){
        min1=min(min1,v[i]);
    }
    cout<<min1;
    return 0;
}