#include<bits/stdc++.h>
using namespace std;
int v0,v1,n,w[505],c[505],dp[10005];
int main(){
cin>>v0>>v1;
int v=v1-v0;
cin>>n;
for(int i=1;i<=n;i++){
cin>>c[i]>>w[i];
}
for(int j=v;j>=0;j--){
dp[j]=0;
}
for(int i=1;i<=n;i++){
for(int j=0;j<=v;j++){
for(int k=0;k*w[i]<=j;k++) {
if(dp[j]!=0) dp[j]=min(dp[j],dp[j-w[i]*k]+c[i]*k);
else dp[j]=dp[j-w[i]*k]+c[i]*k;
}
}
}
if(dp[v]==0) cout<<"This is impossible.";
else cout<<"The minimum amount of money in the piggy-bank is "<<dp[v]<<".";
return 0;
}
